Key user Can't get onto my VBulletin Site?

[Brother Malachi]

E-mail your host and have them check mod_security logs. Look up the IP of the guys that can't get on and send them to your host's techs.
There is a rule in there that gets triggered and bans a user from the site on a hacking suspicion when they utilize the POST function in certain situations. A lot of our users got blacklisted this way and we had to manually unban/unblock them and remove the mod_security rule. Have your host's tech look up the rule number and remove it.
Google "mod_security vbulletin" for more info on this.